Rather than the traitor as Judas is portrayed in the New Testament, The Gospel of Judas indicates that he acted at the request of Jesus to help him shed his earthly body.
Elaine Pagels, a professor of religion at Princeton University, said that "the people who loved, circulated and wrote down these gospels did not think they were heretics".
Terry Garcia, of the National Geographic Society, which made the manuscript public, said it was probably written around AD300 in Coptic script and was a copy of an earlier Greek manuscript.
The manuscript was discovered in
a desert cave in Egypt
The papyrus script, known as a codex, was found in the desert in Egypt in the 1970s and has now been authenticated by carbon dating and studied and translated by biblical scholars, National Geographic announced.
Garcia said: "The codex has been authenticated as a genuine work of ancient Christian apocryphal literature on five fronts: radiocarbon dating, ink analysis, multispectral imaging, contextual evidence and paleographic evidence."
Unlike the four gospels in the Bible, this text indicates that Judas betrayed Jesus at Jesus's own request.
The text begins with "the secret account of the revelation that Jesus spoke in conversation with Judas Iscariot".
The key passage comes when Jesus tells Judas: "You will exceed all of them. For you will sacrifice the man that clothed me."
Scholars said this indicates that Judas would help liberate the spiritual self by helping Jesus get rid of his body.
Garcia said the codex "enhances our knowledge of the history and theological viewpoints of the early Christian period".
The manuscript was first mentioned in a treatise in around AD180 by Bishop Irenaeus of Lyon. The bishop denounced the manuscript as differing from mainstream Christianity.
There were several gospels in circulation at the time in addition to the four in the Bible. When those gospels were denounced, it was thought that believers hid them away.
The gospel of Judas was kept by a group called the Gnostics, who believed that the way to salvation was through secret knowledge given by Jesus to his inner circle.
National Geographic said the author of the gospel of Judas believed that Judas Iscariot alone understood the true significance of Christ's teachings.